A model is a concept showing the change in state from before and after a change is made. It is an attempt to visualize and predict the change. Since in the real world each system is unique, a good deal of effort has been taken to provide generic change models that can be used as the foundation for presenting proposed change or change analysis in real situations. It was not always easy to draw an abstract change concept however most of the diagrams are quite good at depicting the concept and certainly can be used as a foundation and starting point for modeling a rea-world tangible scenario.
In many ways these models are the core action of the framework. Using the models and the rest of the framework together provides real-world actions to improve teams of people as well as conceptual context to justify the proposals.
The models are present in no order of precedence.